The present invention relates to a coupling apparatus for connecting coaxial cables, which are lines for transmitting a high-frequency energy, and more particularly, to a coupling apparatus for coaxial cables capable of connecting radio equipment components to each other, the equipment components being provided inside and/or outside a closed space such as an interior of a room, vehicle and the like. The present invention further relates to an antenna system using the coupling apparatus between coaxial cables described above.
A mobile radio communication system, which is loaded on an automobile or vehicle, is configured from a radio apparatus main body loaded on an interior of the vehicle, an antenna provided on an outer surface of the vehicle for transmitting and receiving radio wave, and a coaxial cable for connecting the radio apparatus main body and the antenna. The coaxial cable extends from the interior of the vehicle to the outside of the vehicle to be connected with the antenna. Two known methods of connection include opening a hole for passing through the coaxial cable, other is to cause the coaxial cable to pass through a gap between a body and a door of the vehicle by using a partially narrow coaxial cable. In the same manner, when an outdoor reception antenna is connected to a radio apparatus such as a television receiving set which is positioned in the interior of a house, a coaxial cable is wired through a hole opened in a part of the house or a gap such as a window for connecting the antenna and the radio apparatus.
Opening a hole through the vehicle body is a troublesome matter and the hole causes the property value of the vehicle to be reduced. Using the gap between the body and door has the possibility for cutting the coaxial cable. Furthermore, it is the problem that there are draft noises and rain leaks through the hole and gap.
Likewise, it is troublesome to open the through-hole in ferro-concrete buildings in the later. Furthermore, a tenant is not generally permitted to open the hole through the wall in the case of a rented house or an apartment complex.
Accordingly, there is provided a method of connected coaxial cables without opening a hole through the vehicle body or wall, in which an antenna is mounted on the window glass, capacitance coupling portions are formed by electrodes attached on both side of the window glass, and high-frequency signals are supplied from the antenna through the outside coaxial cable, the capacitance coupling portions and the inside coaxial cable. FIG. 1A shows an example of an antenna apparatus of KG144 type produced by Lasen Electronics Inc. in USA. The antenna apparatus comprises a capacitor 2 connected to a central conductor of a coaxial cable 4 and a capacitor 3 connected to an outer conductor of the coaxial cable 4. The capacitor 2 is configured from a pair of rectangular electrodes 2a which are provided at both sides of a glass plate 1 in the manner of opposing each other. The capacitor 3 is configured from a pair of rectangular electrodes 3a which are provided at both sides of the glass plate 1 in the manner of opposing each other. The capacitor 2 is connected through a capacitor C to an end of an outer antenna 300. The capacitor 3 is connected through an inductor L to the outer antenna 300.
FIG. 1B shows an example of an antenna apparatus of an AP143 type produced by Avanti in USA. The antenna apparatus uses a capacitor 2 including electrodes 2a which oppose each other through a glass plate 1. One electrode 2a of the capacitor 2 is connected to an antenna 300, and the other electrode 2a is connected to an inner conductor of a coaxial cable 4. An outer conductor of the coaxial cable 4 is connected to the inner conductor of the coaxial cable 4 through an impedance circuit including an inductor L and capacitor C.
Furthermore, there is a glass passing type antenna (not shown) for an automobile radio receiver, as another example of such a glass passing type antenna, which is disclosed in the official gazette of Japanese Patent Laid-open No. 3-34704 (1991). The antenna uses an LC multipletuned circuit of an electromagnetic coupling which are formed at both sides of a glass plate for frequency modulated (FM) signals, while the antenna uses a capacitor and FET amplifier formed at both sides of the glass plate for amplitude modulated (AM) signals, thereby transmitting a high-frequency signal inside and outside of the cabin.
However, even though such kinds of conventional antenna apparatus have coaxial cables which are wired near the inner surface of the glass plate, it is impossible to transmit a high-frequency energy while maintaining a coaxial transmission mode to the outer antenna apparatus outside the glass plate.
As a result, an impedance matching is not balanced well between the coaxial cable 4 and antenna 300. An antenna current flows into the outer conductor of the coaxial cable 4, so that it is easy to generate a so-called radio wave leakage from the coaxial cable. A transmission efficiency of the high-frequency power decreases. Particularly, the conventional apparatus have the problem that it is difficult to actually use the apparatus in a land mobile radiotelephone, a combined use radio telephone apparatus as a mobile and portable set, and a compact transceiver which are required the high transmission efficiency because they only have a low transmission power.
Since the glass passing type antenna apparatus of such a kind is limited an attached position of the antenna onto the glass surface, an antenna of the desired kind is required to be set to the proper position such as a roof of the vehicle by extending the coaxial cable along the body surface. In same manner, in the buildings, it is required to set an antenna of the most fitted kind to the proper position such as a balcony or roof without a window glass. Furthermore, it is desired to connect a plurality of antennas for performing a diversity receiving system and corresponding to a plurality of broadcasting stations in the different directions, to the coaxial cables in the transmission reception apparatus through the glass plate.